The PD-1 expression balance between effector and regulatory T cells predicts the clinical efficacy of PD-1 blockade therapies

Checkpoint blockade is effective in only a subset of patients; therefore, biomarkers that can predict efficacy would be clinically highly valuable. Nishkawa and colleagues develop a biomarker based on PD-1 positivity of effector and regulatory T cells in the tumor microenvironment that accurately predicts the effectiveness of checkpoint blockade in patients. Immune checkpoint blockade has provided a paradigm shift in cancer therapy, but the success of this approach is very variable; therefore, biomarkers predictive of clinical efficacy are urgently required. Here, we show that the frequency of PD-1(+)CD8(+)T cells relative to that of PD-1(+)regulatory T (T-reg) cells in the tumor microenvironment can predict the clinical efficacy of programmed cell death protein 1 (PD-1) blockade therapies and is superior to other predictors, including PD ligand 1 (PD-L1) expression or tumor mutational burden. PD-1 expression by CD8(+)T cells and T(reg)cells negatively impacts effector and immunosuppressive functions, respectively. PD-1 blockade induces both recovery of dysfunctional PD-1(+)CD8(+)T cells and enhanced PD-1(+)T(reg)cell-mediated immunosuppression. A profound reactivation of effector PD-1(+)CD8(+)T cells rather than PD-1(+)T(reg)cells by PD-1 blockade is necessary for tumor regression. These findings provide a promising predictive biomarker for PD-1 blockade therapies.